Effects of temperature on the growth of lettuce (Lactuca sativa L.) and the implications for assessing the impacts of potential climate change

Abstract Stands of lettuce were grown from a single transplanting in the field within two double-walled polyethylene tunnels along which temperature gradients were imposed. Plant dry weight was initially higher in the warmer plots, but maximum dry weight of lettuces grown under cooler condi tions was ultimately higher. Plant relative growth rate declined during ontogeny. This decline increased with increasing temperature. A simple growth model of this response is described in which the optimum incident radiation and optimum temperature for instantaneous relative growth rate are constant. but the maximum potential relative growth rate declines with developmental thermal time. This model was optimized using data from two plots, and predicted accurately the observed increase in the dry weight of lettuce grown in 14 independent plots. The potential effects of six scenarios of climate change on the yield of lettuce grown from this transplanting date was assessed using this model. Calculated maximum yields, averaged over 15 years, ranged only between a 6 per cent reduction and a 5 per cent increase compared to the present baseline climate depending on which climate change scenario was used. The time from transplanting to a lettuce of marketable fresh weight was reduced (by up to 9 days) under all six scenarios.